This invention is directed, in general, to a monitoring device; and, in particular, this invention relates to a device for monitoring the axial displacement of a rotating shaft.
One example of an advantageous application of the present invention is within the environment of a large turbomachine such as a steam turbine. A steam turbine is a fluid driven machine comprised of a fluid tight casing having a rotating shaft (rotor) mounted therein. At either end of the casing the rotor is rotatably supported in a journal bearing. The rotor comprises a series of bladed rings which extend radially outward from the rotor in increasing diameters along the length of the rotor. Each blade ring is interposed between radially inwardly extending diaphragm rings which are stationary. Thus, a flow path through the casing is defined. For optimum efficiency, axial clearances between the rotating blade rings and the stationary diaphragm rings are expressed in mils and such clearances must be rigorously maintained. The axial position of the rotor is maintained in either direction by a thrust bearing in association with a thrust collar rotatable with the rotor. The interface between the thrust collar and the thrust bearing is comprised of an oil film.
Over an extended period of operation some wear of the thrust bearing will occur and permit some limited axial displacement of the rotor in either direction. It is important to note such axial displacement prior to the occurrence of real damage to the turbine parts previously mentioned so that routine maintenance procedures may be followed. In the event such axial displacement becomes excessive, then it may be desirable to automatically trip the turbine.
Prior art devices include U.S. Pat. No. 3,220,244 to Donnelly. In that patent, the preferred embodiment utilizes oil as a working fluid and includes a differential pressure gauge connected to an alarm or tripping device. The present invention differs in the manner in which the tripping and alarm circuits are implemented and moreover the present invention is fully testable. U.S. Pat. Nos. 2,888,023 and 3,861,818, both to Eggenberger show electrohydraulic devices which differ from the present invention both in construction and in the mode of operation and, which are not particularly suitable for retrofit applications.